Preheat your oven to 350°F and prepare an 8x8-inch baking pan by lining it with parchment paper, allowing some paper to hang over the edges.

In a medium saucepan on low heat, melt the butter and 4 ounces of the chopped chocolate. Stir continuously until smooth. Remove from heat and transfer to a large mixing bowl.

Mix in the sugars and whisk until well blended. Let cool slightly, then add the eggs one at a time, whisking after each addition. Stir in the vanilla extract.

In another bowl, combine the flour, cocoa powder, and salt. Gradually fold the dry ingredients into the wet mixture. Add in the remaining chocolate pieces and stir until just combined.

Spread half the brownie batter into the prepared pan. Drop 1/4 cup of peanut butter on top, then layer the rest of the batter over it. Drizzle the remaining peanut butter on top and gently swirl with a knife.

Bake for 35-40 minutes. Check for doneness by ensuring the edges are firm and the center doesn’t jiggle. If the top browns too quickly, cover with foil.

Cool completely in the pan on a wire rack. Once cooled, lift the brownies out using the parchment overhang and slice into squares. Serve and enjoy!